The present invention relates to a brake actuating unit for actuating a motor vehicle brake system of the ‘brake-by-wire’ type comprising:
a) a brake booster which is operable in response to the driver's wish both by means of a brake pedal and by means of an electronic control unit, and a means is provided to decouple a force-transmitting connection between the brake pedal and the brake booster in the ‘brake-by-wire’ operating mode,
b) a master brake cylinder connected downstream of the brake booster,
c) a means to detect a deceleration request of the driver, and
d) a pedal travel simulator which interacts with the brake pedal and due to which a resetting force acting on the brake pedal can be simulated in the ‘brake-by-wire’ operating mode independently of an actuation of the brake booster, and which can be enabled in the ‘brake-by-wire’ operating mode when the force-transmitting connection between the brake pedal and the brake booster is decoupled and can be disabled outside the ‘brake-by-wire’ operating mode.
An actuating unit of this type is disclosed in DE 197 50 977 A1. The pedal travel simulator in the prior art brake actuating unit cooperates with a two-part piston operable by the brake pedal, the piston parts thereof being isolated from each other so that their mechanical decoupling can be realized in the ‘brake-by-wire’ operating mode. A component furnished with a slope is displaceably arranged on the first piston part associated with the brake pedal, said component being moveable into engagement with another component on which a simulator spring is supported. The second piston part is in a force-transmitting connection with a movable wall of the brake booster. The pedal travel simulator is enabled by the component furnished with the slope engaging the additional component used to support the simulator spring. In emergency situations, for example, in power failure, mechanical connection between the two piston parts is established, whereby the pedal travel simulator is disabled.
It is, however, disadvantageous in the prior art actuating unit that force transmission does not take place between the first piston part and the sloped component at high brake pedal depression speeds so that the pedal travel simulator is not enabled. Further, a change from ‘high-μ’ to ‘low-μ’ causes uncoupling of the pedal travel simulator and coupling of the brake booster to the brake pedal, with the result that abrupt changes in force can be felt at the brake pedal.